Potentiometer



M. A. AYOUB POTENTIOMETER July 30, 1963 2 Sheets-Sheet 1 Filed NOV. 18, 1960 FIE-5.1

7% arlzeg/i M. A. AYOUB POTENTIOMETER July 30, 1963 2 Sheets-Sheet 2 Filed NOV. 18, 1960 v 'I'IIIIIIIIIIIIA 3 L W Z? Unite 3,li99,811 PUTENTHUMETER Michael A. Ayouh, Needliarn, Mass, assignor to Waters Manufacturing, line, Wayland, Mass, a corporation of Massachusetts Filed Nov. 18, 196i Ser. No. 70,3M 8 Claims. (til. 338-474) This invention relates to a potentiometer and, more particularly, to an improved construction for a miniature precision potentiometer which is capable of simple assembly and to a method of assembling such a potentiometer.

Precision potentiometers, as such, are delicate instruments, which ordinarily require extreme care in their assembly to maintain high standards of quality. Miniature precision potentiometers normally require even a greater standard of care and high caliber workmanship in their assembly, so that the cost of assembling miniature potentiometers is generally substantial. It is, therefore, the principal object of the instant invention to provide a construction for a miniature potentiometer which enables easy but accurate assembly, thereby reducing the cost of manufacture, and at the same time to provide a construction employing parts of simple and inexpensive construction without impairing the ultimate precision of the potentiometer in use.

A number of simplifications and cost-reduction features are combined in the present potentiometer construction, while preserving, or even enhancing, performance characteristics. The nature of these features, and other objects and advantages of the invention, will become readily apparent to those skilled in the art upon perusal of the description of an embodiment thereof shown in the drawings, in which:

FIGUE 1 is a cross-sectional view of a potentiometer embodying the invention;

FIGURE 2 is a plan view of the back of the potentiometer shown in FIGURE 1;

FIGURE 3 is an enlarged fragmentary cross-sectional view showing the details of construction of a brush assembly in contact with a resistance element and a slip ring in the potentiometer;

FIGURE 4 is a cross-sectional view taken on line 4-4 of FIGURE 1;

FIGURE 5 is a plan view of the front of the potentiometer shown in FIGURE -1;

FIGURE 6 is a plan view of a combined stop member, torque device and shaft positioner which is a part of the potentiometer shown in FIGURE 1;

FIGURE 7 is a partial cross-sectional view taken on line 7-7 of FIGURE 6;

FIGURE 8 is a plan View of a slip ring and terminal assembly employed in the fabrication of the potentiometer; and

FIGURE 9 is a cross-sectional view taken on line 9-9 of FIGURE 8.

Referring now to the drawings and especially to FIG- URE l, the potentiometer indicated by numeral 1t) consists generally of a molded plastic housing 112 with a wirewound resistance element 16 mounted in the housing, a wiper assembly 18 in sliding spring pressure contact with the resistor, a shaft 20 mounting the assembly 18 and a stop member 22 abutting a fixed stop on the housing to limit the rotation of the shaft 20.

The housing 12 consists of a base 24 and a cover 26. Both the base and the cover are made of a molded insulating plastic, and having mating surfaces. The base 24 has a floor or front wall 28 and a side wall 30. The side wall 30 has three grooves 32 passing the electrical terminals to be later described. The base also has a resistor groove or shoulder 34 which receives the res ist- Patented July 30, 1963 ice ance element 16. A slip ring mounting boss 36 is formed integrally with the floor 28 to provide with the side wall a slip ring mounting recess 37, and a central recess or shoulder 46 is formed in the boss 36. Extending axially along the boss 36 and through floor 2-8 is a sleeve bushing aperture 38 which receives shaft 20 as will be described hereinafter. The side wall 30* includes a shouldered portion 42 which mates with a similar shouldered portion 44 of cover 26 for a sealing relation between the base and the cover.

The cover 26 includes a back wall 46 and a side wall 48, an inwardly extending stop 50 being formed on the inner surface of the side wall. Three lugs 52 are formed on the outer surface of the side wall 48, equiangularly spaced about the periphery, as may be seen in FIGUREZ.

The housing 12 is generally cylindrical in configuration, with a generally rectangular terminal ledge 54, consisting of a base ledge 56 having the aforementioned grooves 32 and a mating cover ledge 58.

The resistance element 16 is conventional in construction, including a resilient mandrel 66 with a fine resistance wire 62. wound thereon. The mandrel with the resistance wire is slightly greater in free diameter than the resistor groove 34 in the base 24 so that the resistor, when slipped into the circular groove, is held securely by the resilience of the mandrel. A bushing 64 is fixed to the base 24. The bushing includes a tubular head 66 which fits through aperture 38 and is flared onto the shoulder 4!) to afiix the bushing to base 24. The bushing also includes an integral hexagonal head 68 which seats in a matching recess on the outer surface of floor 28 so that the bushing is securely held in position against rotation. The bushing has a threaded shank 7t) slotted at the outer end to permit use of a shaft-locking nut, if desired. The bushing forms an axial shaft aperture or bearing 72 for the shaft 20.

A groove 74 is formed adjacent to the exterior end of bushing 64 as may be seen in FIGURE 1, and a C-ring 76 is mounted in the groove to limit inward motion of the shaft. The free end of the shaft has a screwdriver slot 77. The shaft also has a second groove 78 which has an O-ring 88} mounted therein to form a seal with the interior of the bushing. The end of the shaft which extends within housing 12 has flats formed on opposite sides of end 81. A washer 82 having an aperture fitting the fiatted portion 81 of shaft 20 is positioned on that end in sliding engagement with the flared end of tubular head 66. An insulating carrier bushing 84 having a similar aperture 85 is mounted next to the washer to rotate with the shaft, being recessed to receive the washer.

The stop member 22 is mounted on the flatte-d end 81 adjacent to the carrier bushing 8 As may be seen in FIGURES 6 and 7, the stop member 22 has a mounting aperture 86 similar to the apertures in the other members mounted on the flatted portion of the shaft. The stop member includes a pair of spring ears 8% which extend radially and rearwardly to engage the inside of the cover to provide frictional torque in operation by friction between the friction surfaces so engaged and also to exert outward thrust on the shaft, .thus aiding in obtaining secure seating of the wiper on the resistance element, the C-ring 76 thus being normally apaced from the bushing 64, as in the drawing. The stop member also has a stop arm integral with the cars 88 and engageable with the stop 50 to limit the rotation of the shaft 23 in both directions, the ears 88 being sufiiciently shorter than the arm 90 to clear the stop St) in rotation.

A brush arm 92, which is best shown in FIGURES 3 and 4, has a substantially square central opening 94 which receives a correspondingly shaped contact mounting boss 96 of the bushing 84, so that the brush 92 rotates with the bushing and the shaft 20. The brush 92 has a more or less conventional wiper portion 98 which engages the resistor 15, but it will be noted that the wiper or brush 92 may be of simpler and cheaper construction than that normally required for satisfactory life and noisefree operation in a potentiometer of comparable precision, for reasons later to be noted. In the present instance the contact is formed integrally with the spring support portion.

A pair of spring arms 1% are formed integrally with the Wiper 98 and extend downward from the wiper to contact a slip ring 102. As previously indicated, the spring ears 88 tend to urge the wiper and the spring arms of the brush into tight electrical contact with the resistor and slip ring, respectively, the force exerted by the ears 88 being much greater than the opposite force exerted by the wiper assembly, thus normally holding the shaft in the outermost position illustrated in the drawing, the corners of the square boss 9'4, abutting the boss 36.

The slip ring 102 has a mounting aperture 1&4 formed with a plurality of prongs 1116 extending therein. The slip ring is pressed onto boss 36, the prongs 1% gripping the boss 36 so that the slip ring is securely held in place. The slip ring has a slip ring terminal 108 integral therewith and extending out through the terminal ledge. Terminals 110 and 112 have bent tabs 113 and 115 in electrical contact with the ends of the resistor 61) as may be seen in FIGURE 4 and all of the terminals 108, 110 and 112 extend outward, parallel and coplanar, through the terminal ledge 54, an offset 117 between the slip ring 102 and its terminal 168 producing this relation.

An anti-rotation plate 114 is mounted on the base of the housing. The anti-rotation plate has a central apermm 116 passing the threaded shank 70 of the bushing and a pair of ears 118 are stamped rearwardly out of the plate adjacent to the aperture 116 for engagement with the nut 68 to hold the plate rotationally. The plate 114 has three apertured arms 120' equiangularly spaced and extending outwardly and rearwardly and bent over into engagement with the lugs 52 on cover 25 to hold the cover 25 in engagement with the base 24, being latched into position by the pressure exerted by the spring arms 88 on the interior of the cover.

It will be seen that the potentiometer 10 may be quickly and conveniently assembled as a unit involving a minimum of operations without loss of accuracy. As was mentioned above, the bushing 64 has its annular head 66 positioned in aperture 38 of base 24. The annular head is bent over by a pressing or peening operation to deform the head to the position shown in FIGURE 1, so that the hexagonal nut 68 rests in the recess provided and the bushing is held securely in position.

Initially, the terminals 108, 110 and 112 are formed by a stamping operation in a unitary structure 126 with a head or connecting portion 127 connecting the parallel terminals as shown in FIGURES 8 and 9. The unitary structure 126 is positioned on the base 24 and the slip ring 102 is pressed over boss 36 into the slip ring recess in the base, being secured therein by the prongs 106 which become embedded in the boss 36, the terminals 108, 110, and 112 being secured in grooves 32 by suitable resin.

The resistor 62 is positioned in the base 24- with the ends of the resistor in electrical contact with the upwardly bent ends or tabs 113 and 115 on terminals 110 and 112. In order to position the resistor in the resistor mounting recess, the generally toroidal shaped mandrel is slightly compressed and positioned in the recess of the base and then released so that the resilience of the mandrel holds the resistor in position and holds the ends of the resistance element in tight electrical contact with tabs formed on the inner ends of terminals 110 and 112 radially outward of slip ring 102.

The washer 82. is positioned within boss 96 of the bushing 84, and the square hole 94 in the brush 2 is press fitted onto the square boss 96, this assembly being placed on the tlatted end 81 of the shaft. The stop member 22 is then positioned on the shaft, and the end of the shaft is pressed or peened so that the shaft end is enlarged by deformation and the stop member, bushing and Washer are locked in position on the shaft. The shaft 213 is inserted in the bushing 26 and lock ring 76 is placed on the groove 74 on the shaft.

With the shaft and spring arms held in position, the anti-rotation plate 114- is positioned with the ears 118 in engagement with nut 68. The cover 26 is then placed in mating engagement with base 24 and pushed on against the force of the resilient spring ears 88 and the arms 12%) are hooked over the lugs 52 as shown in FIG- URE 1, the force exerted by the ears 88 thus latching the cover securely in position and seating the corners of the boss 96 on the boss 36, ring 76- then being spaced from the end of shank 7d and the wiper and the spring arms being simultaneously urged into secure electrical contact with the resistor and the slip ring respectively. Thus the spring ears provide a dual function in the static condition by simultaneously locking the cover into engagement with the plate 114 and holding the wiper and spring arms in secure electrical contact, thus producing reliable noise-free operation, in addition to providing the locking torque necessary to hold the adjustment of the potentiometer against vibration, etc.

After the cover is placed in position, the head 127 of the terminal unit is snipped off so that the terminals are each individual and separate and mutually insulated.

in the operation of the instant potentiometer, it may be seen how the present construction reduces wear on the moving contact and resistance element. A screwdriver is used to adjust the setting of the wiper relative to the resistor. When an operator inserts the blade of a screwdriver into slot 77, normally he pushes the blade inward and simultaneously rotates the shaft. It is apparent that when a force is applied to force 21) inward the shaft moves axially into the housing. The axial movement of the shaft also reduces wiper pressure so that as the wiper rotates with the shaft, the frictional contact between the wiper and resistor is smaller than in the static position.

Thus in addition to the functions served by the spring arm portions of the stop member in the static condition, the unitary stop member acts in the course of adjustment of the potentiometer to relieve the wiper pressure, thus reducing wear on the wiper without any sacrifice of security of contact in the steady state operation of the potentiometer. The C-ring '76 forms a limit stop on inward motion of the shaft, assuring that the wiper contact, although lessened in frictional engagement, remains in contact with the resistance element under the force of the spring portion of the wiper. It will also be seen that the illustrated construction permits broad dimensional tolerances in the shaft-mounting parts without introducing free end-play of the shaft.

While a specific embodiment of the construction and a specific embodiment of the method of making a potentiometer are disclosed herein, it will readily be appreciated that those skilled in the art will be able to make variations and modifications in the illustrated construction and method without departing from the spirit and scope of the invention. It should therefore be understood that the scope of the present invention is limited only to the appended claims.

What is claimed is:

In a potentiometer, a stationary portion comprising an enclosure containing a resistance element and having front and back walls, and a rotary portion comprising a shaft extending through the front wall of the enclosure, a movable contact, and means for mounting the contact on the shaft, said mounting means including a spring portion urging the contact in a first axial direction to contact with the resistance clement, stop means on the shaft and on one of said walls of the enclosure limiting motion of the shaft in said first axial direction, the shaft being free for motion in the opposite axial direction, and spring means of greater force than said spring portion acting between the rotary portion and the stationary portion of the assembly to urge the shaft in said first axial direction, whereby the spring means normally holds the shaft at the limit of the motion fixed by the stop means to exert the full force of the spring portion of the contact-mounting means on the contact.

2. The improved construction of claim 1 wherein the spring means comprises a spring member affixed to one of the portions and in sliding contact with the other to produce frictional locking torque.

3. The improved construction of claim -1 wherein the back wall of the enclosure has a stop projection thereon and the spring means comprises a member on the shaft having portions extending rearwardly to contact the back wall, the stop projection being radially displaced from the rotational path of said portions, and the member on the shaft having an additional portion having the stop projection in its rotational path to limit rotary motion.

4. A potentiometer comprising a housing having separable front and back portions, a shaft extending into the housing through the front portion, a resistance element and a contact within the housing, the contact being mounted to be slidingly adjusted upon rotation of the shaft in spring-pressure contact with the element, radially protruding lugs on the exterior of one of the portions of the housing, apertured arms extending in the axial direction from the other portion, the lugs extending radially through the apertures in the arms, and engaging the lugs, friction surfaces rotationally affixed to the back portion of the housing and to the shaft, respectively, and spring means of greater force than said spring pressure, urging the friction surfaces into frictional contact and urging the front and back portions apart, whereby the spring means simultaneously provide frictional torque to the potentiometer and urge the portions of the housing in opposite directions to latch the lugs into the arms to secure the two portions of the housing.

5. The potentiometer of claim 4 wherein the friction members have stop members formed thereon and integral therewith, the stop member on the housing being in the rotational path of the stop member on the shaft, but radially displaced from the rotational path of the friction surface affixed to the shaft.

6. In a potentiometer having a base, a resistance element mounted on the base, a shaft mounted for rotary motion in the base, a movable contact, and first spring means mounting the contact on the shaft for motion along the resistance element and urging the contact against the resistance element in an axial direction, the improved construction comprising second spring means of greater force than the first spring means urging the shaft in said axial direction, and means on the shaft and the base to limit reciprocatory motion of the shaft between a first end position wherein the first spring means exerts greatest force on the contact and a second end position substantially spaced from the first position wherein the first spring means exerts substantially less force on the contact but maintains it against the resistance element, so that the second spring means normally holds the shaft in the first position, but the contact friction in adjustment may be reduced by exterior application of force to the shaft.

7. The potentiometer of claim 6 wherein the second spring means urges the shaft outward, and the outer end of the shaft is constructed and arranged to fit a manual adjusting tool.

8. The potentiometer of claim 4 having a plate overlying the outer surface of the fnont portion of the housing, apertured to pass the shaft, the arms being integral with said plate and extending rearwardly therefrom, the lugs being integrally formed on the rear portion of the housing.

References Cited in the file of this patent UNITED STATES PATENTS 2,389,750 Turner et al Nov. 27, 1945 2,576,044 Richman et al Nov. 20, 1951 2,781,436 Barden Feb. 12, 1957 2,916,717 Hartman et a1. Dec. 8, 1959 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,099,811 July 30, 1963 Michael A. Ayoub It is hereby certified that error appears in the above numbered paten't requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 68, for "having" read have column 2, 11ne 63, for "apaced" read spaced column 5, line 30, strike out "and engaging the lugs.

Signed and sealed this 25th day of Feb-nuary 1964.

(SEAL Attest:

ERNEST W. SWIDER EDWIN L iIE'L'Y-JOLDS Attesting Officer AC L g Commissioner of Patents 

1. IN A POTENTIOMETER, A STATIONERY PORTION COMPRISING AN ENCLOSURE CONTAINING A RESISTANCE ELEMENT AND HAVING FRONT AND BACK WALLS, AND ROTARY PORTION COMPRISING A SHAFT EXTENDING THROUGH THE FRONT WALL OF THE ENCLOSURE, A MOVABLE CONTACT, AND MEANS FOR MOUNTING THE CONTACT ON THE SHAFT, SAID MOUNTING MEANS INCLUDING A SPRING PORTION URGING THE CONTACT IN A FIRST AXIAL DIRECTION TO CONTACT WITH THE RESISTANCE ELEMENT, STOP MEANS ON THE SHAFT AND ON ONE OF SAID WALLS OF THE ENCLOSURE LIMITING MOTION OF THE SHAFT IN SAID FIRST AXIAL DIRECTION, THE SHAFT BEING FREE FOR MOTION IN THE OPPOSITE AXIAL DIRECTION, AND SPRING MEANS OF GREATER FORCE THAN SAID SPRING PORTION ACTING BETWEEN THE ROTARY PORTION AND THE STATIONARY PORTION OF THE ASSEMBLY TO URGE THE SHAFT IN SAID FIRST AXIAL DIRECTION, WHEREBY THE SPRING MEANS NORMALLY HOLDS THE SHAFT AT THE LIMIT OF THE MOTION FIXED BY THE STOP MEANS TO EXERT THE FULL FORCE 